Re: Reasoning behind LWLOCK_PADDED_SIZE/increase it to a full cacheline

Andres Freund <andres@2ndquadrant.com> writes:
> So, what we do is we guarantee that LWLocks are aligned to 16 or 32byte
> boundaries. That means that on x86-64 (64byte cachelines, 24bytes
> unpadded lwlock) two lwlocks share a cacheline.

Yup.

> In my benchmarks changing the padding to 64byte increases performance in
> workloads with contended lwlocks considerably.

At a huge cost in RAM.  Remember we make two LWLocks per shared buffer.

I think that rather than using a blunt instrument like that, we ought to
see if we can identify pairs of hot LWLocks and make sure they're not
adjacent.
        regards, tom lane